1. Technical Field
The present invention relates to portable electronic equipment and a control method for the electronic equipment, and in particular to electronic equipment and a control method for the electronic equipment with which a power saving mode and a normal operating mode can be switched over depending on a condition of use of the electronic equipment by the user. More specifically, the present invention relates to a timepiece and a control method for the timepiece which can indicate the time with high accuracy for a long time without replacing a battery.
2. Background Art
Recently, small size electronic watches such as wristwatches incorporating power generators, e.g., solar cells, and operating with no need of replacing batteries, have been developed as one form of electronic equipment. Those electronic watches have a function of charging electric power generated by power generators in large-capacity capacitors, and indicate the time with the power discharged from the capacitor when power is not generated. The electronic watches can therefore operate with stability for a long time without batteries. In consideration of the inconvenience of replacing batteries and a problem in disposal of exhausted batteries, it is expected that power generators will be incorporated in more and more electronic watches in future.
Meanwhile, a power generator incorporated in a wristwatch, etc. comprises a solar cell for converting irradiated light into electric energy, or a power generating system for converting kinetic energy, e.g. produced upon motion of the user's arm, into electric energy. Such a power generator is very advantageous in utilizing energy in the user's environment for conversion into electric energy, but has problems in that useable energy density is low and energy cannot be obtained in continuous fashion. Accordingly, power generation can not be performed in a continuous fashion, and the electronic watch operates with the power accumulated in a large-capacity capacitor while the power generation is suspended. For this reason, a large-capacity capacitor is desired, with a capacity as large as possible. A capacitor having too large a size however would raise problems that such a capacitor cannot be accommodated in a wristwatch device, and a proper level of voltage is hard to obtain because a longer time is required for charging the capacitor. On the other hand, if the capacity is too small, the electronic watch would stop operation when power is not generated for a long time. Even if the electronic watch is started again by, for example, irradiating light, the indicated time would be wrong and the precise time would not be indicated. Thus the electronic watch would not fulfill its function.
In a wristwatch device using a solar cell, because the intensity of ambient illumination can be detected with the solar cell, a system is conceived in which when the illumination intensity lowers below a setting value, the time indication is stopped but the time from when indication is stopped is continuously counted by an internal counter, and when the illumination intensity rises, the time indication is resumed and the current time is restored based on a value of the internal counter. With such a wristwatch device, the operation of indicating the time is stopped and energy is saved when the illumination is darkened, e.g., while the user is sleeping, and the time indication is automatically resumed and the current time is restored when it becomes light, e.g. in the morning. Accordingly, the duration of the large-capacity capacitor can be prolonged and the wristwatch can be operated for a long time without inconveniencing the user. Also, by designing a system such that the day-of-time indication is stopped after a certain period of time has elapsed subsequent to a lowering of the illumination intensity, the time can be continuously indicated even if the illumination intensity lowers for a short time as occurs when the wristwatch is hidden under clothes. This system can also save energy without inconveniencing the user.
However, the user often desires to see the time even during the night, and it is inconvenient if the user cannot know the current time instantly on such an occasion. Also, the wristwatch is often not exposed to the sun in the winter during which the user is wearing a coat or the like. If the time indication is stopped under such a condition, the function of the wristwatch is not fulfilled. Conversely, when the user does not wear the wristwatch and leaves it in the room, the time indication continues since the wristwatch is exposed to weak light. This results in wasteful power consumption.
An object of the present invention is therefore to provide electronic equipment and a control method for the electronic equipment with which a power saving mode and a normal operating mode can be switched over depending on a condition of use of the electronic equipment by the user.
Another object of the present invention is to provide a timepiece and a control method for the timepiece which can indicate the time with high accuracy for a long time without replacing a battery.